This invention relates to an improved cutting assembly in the form of a rotary head for a rotary lawn mower, edger, trimmer or the like. The preferred embodiment is in the form of a portable sling-held type lawn mowing and edging tool wherein the cutting element is safe in most uses and avoids the hazardous conditions created by prior art devices. More particularly, the cutting assembly disclosed herein is of the type depicted in U.S. Pat. No. 3,826,068, and is an improvement thereover.
The prior art is prolix with attempts at solutions to provide a safe, efficient, and simply constructed rotary head for rotary lawn mowers, edgers, trimmers and the like. Heretofore, the rotary head, or cutting blade, of rotary lawn mowers, edgers, and the like, have comprised a rotating metal bar or the like which is rotated at sufficient speeds to effect cutting of grass, weeds or the like. However, such bars create hazardous conditions in that when they strike certain objects they act upon those objects in a fashion to create and project dangerous missiles which may strike the operator or individuals in the area of work.
Various attempts have been made to overcome the aforesaid hazardous conditions created with rigid type metal cutting blades of the prior art. Most of these attempts to overcome the problem involve the utilization of some type of flexible flail which will have sufficient resiliency so as not to propel objects which are struck at high velocities. Most of these resilient type cutting elements of the prior art suffer a disadvantage in that they are not safe and mere resiliency is not sufficient to insure that the dangerous conditions will not be created when rotation is effected at desired cutting speeds. Further, the prior art cutting elements are generally not provided with means for easy replaceability in the event of wearing out and are usually expensive to replace.
The result has been that most of the prior lawn edging apparatus have been unsatisfactory because of the dangerous conditions created by the rotating head. As a consequence, most lawn edging and trimming around trees and the like, which would otherwise be damaged by the metal blades, must be done manually, which is both laborious and time consuming.
There is depicted and described in the following West German Petty Pat. Nos. 6,919,841; 6,919,842; 6,919,843; 6,919,844; 6,938,265; 7,043,648; and 7,238,972 one or more embodiments of a lawn mowing or trimming device having a disc-like head member arranged to be rotated by an electric motor, and containing a spool which is housed therein in coaxial relationship to the shaft of the motor. A length of flexible non-metallic line is coiled about the spool, whereby its free travelling end extends generally peripherally from the spool and head, and whereby such free travelling end will be swung arcuately about upon actuation of the motor to cut adjacent vegetation in the manner of a flail.
Use of the German device has revealed that, under ideal operating conditions, it will cut or trim grass and other light-weight vegetation with reasonable effectiveness. Furthermore, it possesses the significant advantage that it is much safer to use than the more conventional cutters, in that it does not cause stones or other solid objects to be discharged in the same dangerous manner, and it is almost completely incapable of causing any significant injury to persons or pets struck by the flailing cutting string. In fact, it is a reasonable statement that the German device will actually cut substantially only the vegetation to which it is directed.
On the other hand, the German device is also subject to certain disavantages of a magnitude such as to severely limit if not destroy its practical value. In the first place, it is largely effective to cut standing light-weight vegetation but is almost completely useless for any other task. In the second place, it will only cut such vegetation if growing relatively sparsely, and it cannot effectively handle even light-weight vegetation if encountered in a rank condition. A more serious disadvantage, however, is that in the German device the cutting string experiences a breakage rate which is so high as to nullify all of its advantages and to keep such a device from having much commercial value.
There is also depicted and described in U.S. Pat. No. 3,826,068 a cutting and trimming device having a housing arranged to be rotated, and containing four spools housed therein. A length of flexible non-metallic line is coiled about each spool whereby the free travelling ends of the four lines extend generally peripherally from the housing and whereby these free travelling ends will be swung arcuately about upon rotation of the housing to cut adjacent vegetation in the manner of flails.
Use of the device of U.S. Pat. No. 3,826,068 has revealed that it will cut or trim grass and other vegetation with maximum effectiveness. Furthermore, like the German device, it possesses the significant advantage that it is much safer to use than the more conventional cutters, in that it does not cause stones or other solid objects to be discharged in the same dangeros manner, and it is almost completely incapable of causing any significant injury to persons or pets struck by the flailing cutting strings. The device of U.S. Pat. No. 3,826,068 will actually cut substantially only the vegetation to which it is directed.
On the other hand, the device of U.S. Pat. No. 3,826,068 is also subject to certain minor disadvantages of a magnitude such as not to limit its practical value but which reduce the efficiency thereof to a slight degree. In the first place, it has been found that the centrifugal force generated upon rotation of the housing causes the spools therein to become misaligned with the compartments housing them. This misalignment problem has been traced to the fact that the thrust springs urging the spools into the compartments are not sufficiently anchored to the lower cup member of the device. Thus, upon rotation of the housing, the thrust springs are moved out of alignment with the axis of the compartment housing each spool. This movement of the thrust spring in turn causes the spool in that compartment to misalign with respect to the axis of that compartment. The resultant misalignment of the spools renders it somewhat difficult to pay out the line members when it is desired to replace the flail portions thereof due to wear. In the second place, it has been found that the coil-like winding of the line member on the spool tends to exert a force on the line member seeking to retract the line member back upon the spool after the line has been payed out to replace the worn flail portion thereof. This is especially true as the amount of line on the spool falls to a minimal length. Thus, the winding of the line upon the spool acts as a spring and when withdrawn from the spool acts with a force to retract a portion of the payed out and extended line member back upon the spool. This retraction of the line member renders it somewhat difficult to maintain a fixed and predetermined length of flail line portion.
One attempt to solve the above line retraction problem has been set forth in U.S. Pat. No. 3,928,911, wherein a pivoted toothed jaw is provided to pinch the line member in place. This device, however, suffers from the serious disadvantage that the pressure of the toothed jaw on the line member injures the line member and produces weakness and flaws therein. Thus, the teeth of the jaw cause internal flaws and indentations in the line member which is highly undesirable, since such flaws and indentations weaken the line and contribute to line breakage as the weakened and indented section is withdrawn and used as the flail portion of the cutting assembly.
It will be readily apparent from a consideration of the teachings hereinafter provided that a cutting string which is free from internal flaws or other defects will not usually break except as a result of being struck against or across a relatively immovable object. The cutting string may, of course, be formed of a metal wire or heavy strap in order to provide it with a tensile strength sufficient to resist such impact, but such a string will create substantially the same dangerous conditions which exist when the cutting element is a rigid blade or the like.
These disadvantages of the prior art are overcome with the present invention, and a commercially acceptable embodiment of a vegetation cutter and the like is herein provided which is not only fully capable of cutting vegetation under most operating conditions, but which is also fully capable of other tasks completely beyond the capabilities of the prior art, such as cleaning dead leaves, trash and other such debris from along fences, walls, and the trunks or stems of trees and bushes. More particularly, however, the embodiment of the present invention is capable of operation with a much lower breakage rate for its cutting strings, without any sacrifice whatsoever of the safety features and advantages hereinbefore accorded to the prior art cutting devices.